online site builder

About us

Atma-Sphere is a small company in Saint Paul, MN that has been making world-class vacuum tube amplifiers since 1976.

We are known for our unique approach to circuit design, resulting in multiple patents and the creation of the first, truly reliable Output TransformerLess (OTL) amplifiers. We made the first balanced-line products in the world of high-end audio, including the MP-1, which was the world's first balanced-line preamp.

All of our amps and preamps are hand-crafted and often optioned according to each customer's needs. Our components are hand-selected; often custom-manufactured especially for us, including our wire.

The resulting products are unique in the world with an unmatched capacity to reproduce music with intrinsic reliability. 

The Absolute Sound interviews Ralph Karsten

Atma-Sphere logo

The reputation of Atma-Sphere

Our key achivements in few words


What is Atma-Sphere all about?

Atma-Sphere was founded in 1978 and is the oldest manufacturer consistently producing OTL (Output TransformerLess) and triode amplifiers. Ralph Karsten designed and patented the music producing circuits which makes our products the best in the world.


Atma-Sphere's claims to fame

The world's first reliable and practical OTL
The world's first fully balanced OTL
The first all triode fully differential zero feedback tube amplifier
The first commercial tube amplifier with only one stage of gain
The most powerful OTL made (the MA-3, producing over 500 watts into 3 ohms)


We also make world class preamps

The world's first fully differential zero feedback all-tube preamp
The world's first all-tube preamp with a direct-coupled balanced output
The world's first and still one of the very few preamps to support the balanced standard (AES48)

Prix et Awards
Ralph Karsten

Ralph Karsten

Ralph Karsten is known for taking the lead in the world of OTL amplifiers; only three patents in the field have been issued since the 1950s and two of those were to Atma-Sphere. Atma-Sphere lead the way with balanced line operation for home use and was the first manufacturer to produce a balanced preamp in 1989, which was also all-tube with a patented direct-coupled balanced output.

Connoisseurs of fine music savour the experience provided by components designed by this master of supreme sound, with over 47 years experience in the audio industry focusing on high end audio.

Video AV Showreports

The CEO of Atma-Sphere presents our products to "AV Showrooms" on YouTube


1742 Selby Avenue
St. Paul, MN 55104


Tel : +1 651-690-2246